/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* pruneTree(TreeNode* root) {
        return dfs(root);
    }

    TreeNode* dfs(TreeNode* node)
    {
        if (node == nullptr) return nullptr;

        node->left = dfs(node->left);
        node->right = dfs(node->right);

        if (node->left == nullptr && node->right == nullptr && node->val == 0) {
            return nullptr;
        }
        return node;
    }

};